The present specification relates to cement-based compositions comprising per 100 parts by weight of cement from 1 to 500 parts by weight of a polymer built up from
a) 30-99.5% by weight of at least one alkyl ester of (meth)acrylic acid,
b) 0-70% by weight of at least one vinylaromatic,
c) 0.5-10% by weight of at least one alkyl polyethoxy(meth)-acrylate of the formula 
where R1 is a hydrogen atom or a methyl group, R2 is a C1 to C4 alkyl group and n is an integer from 1 to 55,
d) 0-10% by weight of at least one ethylenically unsaturated mono- or dicarboxylic acid or anhydride, amide or hydroxyalkylamide thereof,
e) 0-10% by weight of acrylonitrile or methacrylonitrile, and
f) 0-50% by weight of further ethylenically unsaturated compounds other than a) to e).
The properties of hydraulic binders, especially cement, can be improved by adding synthetic polymers. The desire is to increase the flexibility of the binders resulting in improved crack bridging and, consequently, in improved freeze-thaw resistance. Further, polymer additives generally bring about reduced penetration of water and improved adhesion to different substrates.
Suitable polymers are those which are added to the cement in powder form and are present in aqueous dispersion after water has been added. The presence of cement, however, has a deleterious effect on the stability of the aqueous dispersion and results in the formation of coagulum. Therefore, the polymers are required to have very high electrolyte stability.
One possibility for increasing the electrolyte stability of polymer dispersions is copolymerization with surface-active monomers.
The use of polymer dispersions containing surface-active monomers in the polymer as an additive for cementitious materials is described in DE-A-2051569. Mention is made inter alia of esters of carboxylic acids with polyalkylene oxides.
JP-53126093 describes polymer dispersions which can contain ethoxylated (meth)acrylates. The degree of ethoxylation of the (meth)acrylate is from 4 to 30 and the end group on the ethylene oxide chain is a hydroxyl, methyl or alkylaryl group. Addition to cement is one of the uses referred to.
JP-10195312 likewise describes polymer dispersions which can contain hydroxyl-terminated, alkoxylated (meth)acrylates. The polymers are used as an additive for cement.
JP-08217808 describes polymer dispersions having multiphase latex particles, and mixtures thereof with cement. The shell of the latex particles consists of a copolymer containing from 0.05 to 70% of an ethoxylated (meth)acrylate. In the examples, polyethylene glycol monomethacrylate is used.
The use of the alkoxylated (meth)acrylic acid derivatives described above as comonomers results generally in adequate electrolyte stability of the polymers. A disadvantage in many cases, however, is the increased incidence of coagulum formation in the polymer dispersions. Increased coagulum formation makes it more difficult to filter and spray-dry the dispersions. A further disadvantage is an increase in viscosity which is associated with the use of alkoxylated (meth)acrylic acid derivatives and which often occurs after the polymers are added to the aqueous cement slurry. Finally, when relatively large amounts of alkoxylated (meth)acrylic acid derivatives are used, it is common to observe a severe reduction in the strength of the polymer-modified cement materials.
It is an object of the present invention to provide polymer-modified cement compositions in which the polymer has sufficient electrolyte stability. The polymer dispersion used as additive should have a very low coagulum fraction and should be readily convertible to powder form by spray drying. Further requirements are very good compatibility and processability with cement. The hardened polymer-cement formulations should combine high strength with adequate flexibility.
We have found that this object is achieved by the compositions defined above and their use.
The compositions of the invention contain per 100 parts by weight of cement from 1 to 500, preferably from 5 to 250, with particular preference from 10 to 150, parts by weight of the polymer defined in claim 1.
The polymer contains preferably at least 0.8% by weight, with particular preference at least 1% by weight, of the ethoxylated monomer of the formula I (monomer c). In general, the polymer contains not more than 8% by weight, with particular preference not more than 5% by weight and with very particular preference not more than 4% by weight of the monomer c), based on the polymer.
Preferably, the polymer has the following composition:
a) 40-99% by weight, with particular preference from 50 to 98% by weight, of at least one alkyl ester of (meth)acrylic acid,
b) 0-65% by weight, with particular preference from 0 to 60% by weight, of at least one vinylaromatic,
c) 0.8-8% by weight, with particular preference from 1 to 5% by weight, of at least one alkyl polyethoxy(meth)acrylate of the formula I,
d) 0.1-5% by weight, with particular preference from 0.3 to 4% by weight, of at least one ethylenically unsaturated mono- or dicarboxylic acid,
e) 0-8% by weight, with particular preference from 0 to 6% by weight, of acrylonitrile or methacrylonitrile, and
f) 0-40% by weight, with particular preference from 0 to 30% by weight, of further ethylenically unsaturated compounds other than a) to e).
The alkyl esters of (meth)acrylic acid (monomers a) are preferably C1 to C18, with particular preference C1 to C8, alkyl (meth)acrylates, examples being methyl (meth)acrylate, ethyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, tert-butyl (meth)acrylate and 2-ethylhexyl (meth)acrylate. Particular preference is given to methyl methacrylate, n-butyl acrylate, ethyl acrylate and 2-ethylhexyl acrylate.
The vinylaromatics (b) are especially xcex1-methylstyrene and styrene.
Preferred alkyl polyethoxy(meth)acrylates of the formula (I) (monomers c) are those in which R2 is methyl and n is an integer from 5 to 50, with particular preference from 5 to 30.
Suitable ethylenically unsaturated mono- or dicarboxylic acids, anhydrides or amides (d) are, for example, acrylic acid, methacrylic acid, maleic acid, itaconic acid, their amides such as acrylamide or methacrylamide or their hydroxyalkylamides such as methylol(meth)acrylamide. Acrylic acid and methacrylic acid are particularly preferred.
Examples of further monomers (f) are crosslinking monomers, such as divinylbenzene, xcex1-ethylstyrene, butanediol diacrylate, ethyldiglycol diacrylate, hexanediol diacrylate, ureidoethyl methacrylate, ureidoethyl methacrylamide, allyl methacrylate, 3-methacryloyloxypropyltrimethoxysilane, acetoacetoxyethyl methacrylate, diacetoneacrylamide, acrylamidoglycolic acid or methyl acrylamidoglycolate methyl ether. The proportion of crosslinking monomers, if used, is generally below 5% by weight.
The glass transition temperature of the polymer is preferably from xe2x88x9260 to 50xc2x0 C., in particular from xe2x88x9260 to +30xc2x0 C., with particular preference from xe2x88x9230 to +40xc2x0 C.
The glass transition temperature of the polymer can be determined in accordance with customary methods such as differential thermal analysis or differential scanning calorimetry (cf., e.g., ASTM 3418/82, midpoint temperature).
The polymer is prepared preferably by emulsion polymerization and is therefore an emulsion polymer.
Alternatively, it can be prepared, for example, by solution polymerization with subsequent dispersion in water.
In the case of the emulsion polymerization, ionic and/or nonionic emulsifiers and/or protective colloids, and/or stabilizers, are used as surface-active compounds.
A detailed description of suitable protective colloids is given in Houben-Weyl, Methoden der organischen Chemie, Volume XIV/1, Makromolekulare Stoffe [Macromolecular Substances], Georg-Thieme-Verlag, Stuttgart, 1961, pp. 411 to 420. Suitable emulsifiers include anionic, cationic and nonionic emulsifiers. Accompanying surface-active substances used are preferably exclusively emulsifiers, whose molecular weights, unlike those of the protective colloids, are usually below 2000 g/mol. Where mixtures of surface-active substances are used, the individual components must of course be compatible with one another, which in case of doubt can be checked by means of a few preliminary experiments. It is preferred to use anionic and nonionic emulsifiers as surface-active substances. Customary accompanying emulsifiers are, for example, ethoxylated fatty alcohols (EO units: 3 to 50, alkyl: C8 to C36), ethoxylated mono-, di- and trialkylphenols (EO units: 3 to 50, alkyl: C4 to C9), alkali metal salts of dialkyl esters of sulfosuccinic acid, and also alkali metal salts and ammonium salts of alkyl sulfates (alkyl: C8 to C12), of ethoxylated alkanols (EO units: 4 to 30, alkyl: C12 to C18), of ethoxylated alkylphenols (EO units: 3 to 50, alkyl: C4 to C9), of alkylsulfonic acids (alkyl: C12 to C18) and of alkylarylsulfonic acids (alkyl: C9 to C18).
Further suitable emulsifiers are compounds of the formula II 
in which R5 and R6 are hydrogen or C4 to C14 alkyl but are not both hydrogen and C and Y can be alkali metal and/or ammonium ions. R5 and R6 are preferably linear or branched alkyl radicals of 6 to 18 carbon atoms or hydrogen and in particular have 6, 12 or 16 carbon atoms but are not both hydrogen. X and Y are preferably sodium, potassium or ammonium ions, particular preference being given to sodium. Particularly advantageous compounds II are those in which X and Y are sodium, R5 is a branched alkyl radical of 12 carbon atoms and R6 is hydrogen or R5. It is common to use technical-grade mixtures containing from 50 to 90% by weight of the monoalkylated product, an example being Dowfax(copyright) 2A1 (trademark of Dow Chemical Company).
Suitable emulsifiers are also given in Houben-Weyl, loc.cit., Volume 14/1, pages 192 to 208.
Trade names of emulsifiers include, for example, Dowfax(copyright)2 A1, Emulan(copyright) NP 50, Dextrol(copyright) OC 50, Emulgator 825, Emulgator 825 S, Emulan(copyright) OG, Texapon(copyright)NSO, Nekanil(copyright) 904 S, Lumiten(copyright) I-RA, Lumiten E 3065, Disponil FES 77, Lutensol AT 18, Steinapol VSL and Emulphor NPS 25.
The surface-active substance is preferably an alkoxylated, preferably ethoxylated and/or propoxylated, emulsifier or protective colloid. Particular preference is given to an alkoxylated emulsifier. Low molecular mass anionic or nonionic alkoxylated emulsifiers that may be mentioned include for example alkylphenylpolyethoxysulfonates or alkylphenyl polyethoxysulfates, alkyl or alkenyl polyethoxysulfates or alkyl- or alkenylpolyethoxysulfonates, alkylglycerylpolyethoxysulfonates, ethoxylated sulfosuccinic mono- and diesters, alkyl, alkenyl or dialkyl polyethoxyphosphates, ethoxylated singly and multiply ring-sulfonated mono- or dialkylalkyl biphenylyl ethers, ethoxylated xcex1-sulfo fatty esters, ethoxylated fatty acid monoglycerides or fatty acid alkanolamine sulfates, ethoxylated fatty acid esters or fatty acid sarcosides, glycolates, lactates, taurides and isethionates, alkylphenyl polyethoxylates or propoxylates, alkyl or alkenyl ethoxylates or propoxylates, polyalkylene oxide adducts such as ethylene oxide-propylene oxide block copolymers, fatty acid alkylolamidoethoxylates, and ethoxylated fatty acids, fatty amines, fatty acid amides or alkanesulfonamides.
Particular preference is given to alkylphenylpolyethoxysulfonates or -sulfates, alkyl or alkenylpolyethoxysulfonates or -sulfates, alkylphenylpolyethoxylates or -propoxylates, and polyalkylene oxide adducts such as, for example, ethylene oxide-propylene oxide block copolymers.
The surface-active substance is usually used in amounts of from 0.1 to 20 parts by weight, preferably from 0.5 to 10 parts by weight, per 100 parts by weight of monomer to be polymerized.
The resulting polymer dispersion and also the polymer powder obtained in the case of subsequent drying, e.g., spray drying, therefore contain a corresponding amount of the surface-active substance.
Examples of water-soluble initiators for the emulsion polymerization are ammonium salts and alkali metal salts of peroxodisulfuric acid, an example being sodium peroxodisulfate, hydrogen peroxide, or organic peroxides, an example being tert-butyl hydroperoxide, or water-soluble azo compounds.
Reduction-oxidation (redox) initiator systems are particularly suitable.
The redox initiator systems consist of at least one, usually inorganic, reducing agent and one organic or inorganic oxidizing agent.
The oxidizing components comprise, for example, the abovementioned initiators for the emulsion polymerization.
The reduction components comprise, for example, alkali metal salts of sulfurous acid, such as sodium sulfite, sodium hydrogen sulfite, alkali metal salts of disulfurous acid such as sodium disulfite, bisulfite addition compounds of aliphatic aldehydes and ketones, such as acetone bisulfite, or reducing agents such as hydroxymethanesulfinic acid and its salts, or ascorbic acid. The redox initiator systems can be used together with soluble metal compounds whose metallic component is able to exist in a plurality of valence states.
Examples of common redox initiator systems are ascorbic acid/iron(II) sulfate/sodium peroxodisulfate, tert-butyl hydroperoxide/sodium disulfite, tert-butyl hydroperoxide/sodium hydroxymethanesulfinate. The individual componentsxe2x80x94the reduction component, for examplexe2x80x94can also be mixtures, an example being a mixture of the sodium salt of hydroxymethanesulfinic acid and sodium disulfite.
Said compounds are usually in the form of aqueous solutions, the minimum concentration being determined by the amount of water acceptable in the dispersion and the maximum concentration by the solubility in water of the compound in question. In general, the concentration is from 0.1 to 30% by weight, preferably from 0.5 to 20% by weight, with particular preference from 1.0 to 10% by weight, based on the solution.
The amount of initiators is generally from 0.1 to 10% by weight, preferably from 0.5 to 5% by weight, based on the monomers to be polymerized. It is also possible to use a plurality of different initiators for the emulsion polymerization.
In the course of the polymerization it is possible to use regulators in amounts, for example, of from 0 to 0.8 part by weight per 100 parts by weight of the monomers to be polymerized, the function of these regulators being to reduce the molecular mass. Suitable examples include compounds having a thiol group, such as tert-butyl mercaptan, ethylhexyl thioglycolate, mercaptoethanol, mercaptopropyltrimethoxysilane, and tert-dodecyl mercaptan.
The emulsion polymerization takes place in general at from 30 to 130xc2x0 C., preferably from 50 to 95xc2x0 C. The polymerization medium can consist either of water alone or of mixtures of water with water-miscible liquids such as methanol. Preference is given to the use of water alone. The emulsion polymerization can be conducted either as a batch process or in the form of a feed process, including stage or gradient procedures. Preference is given to the feed process, in which a portion of the polymerization mixture is introduced as an initial charge, heated to the polymerization temperature and partly polymerized and then the remainder of the polymerization mixture is supplied to the polymerization zone continuously, in stages or under a concentration gradient while the polymerization is maintained, said supply usually taking place by way of two or more physically separate feed streams of which one or more contain the monomers in pure or in emulsified form. In order, for example, to better establish the particle size, it is also possible to include seed polymer in the initial charge for the polymerization.
Thus it can be particularly advantageous to meter in the ethoxylated (meth)acrylic acid derivative not right at the beginning but only during the course of the emulsion polymerization.
The manner in which the initiator is added to the polymerization vessel in the course of the free-radical aqueous emulsion polymerization is familiar to the skilled worker. It can either be included in its entirety in the initial charge to the polymerization vessel or else introduced continuously or in stages at the rate at which it is consumed in the course of the free-radical aqueous polymerization. This will depend specifically on the chemical nature of the initiator system and on the polymerization temperature. Preferably, one portion is included in the initial charge and the remainder is supplied to the polymerization zone at the rate at which it is consumed.
In order to remove the residual monomers, it is common to add initiator after the end of the actual emulsion polymerization as well, i.e., after a monomer conversion of at least 95%.
In the case of the feed process, the individual components can be added to the reactor from above, through the side or from below, through the reactor floor.
In the case of emulsion polymerization, aqueous dispersions of the polymer are obtained which have solids contents of in general from 15 to 75% by weight, preferably from 40 to 75% by weight.
In order to achieve a high space-time yield of the reactor, dispersions having a very high solids content are preferred. In order to be able to achieve solid contents greater than 60% by weight, a bimodal or polymodal particle size should be established, since otherwise the viscosity becomes too high and the dispersion can no longer be handled. The formation of a new particle generation can be carried out, for example, by adding seed (EP 81083), by adding excess amounts of emulsifier, or by adding miniemulsions. A further advantage associated with the low viscosity and high solids content is the improved coating behavior at high solids contents. The production of a new particle generation or generations can take place at any desired point in time. It depends on the particle size distribution desired for a low viscosity.
The polymer is admixed preferably in the form of powder with the cement.
The polymer powder is preferably dispersible in water (where the polymer is prepared by emulsion polymerization, this is also called redispersibility in water).
Following the emulsion polymerization, the polymer is in the form of an aqueous dispersion of polymer particles.
The average size of the particles is preferably from 50 to 500 nm, with particular preference from 80 to 300 nm. The viscosity of the polymer dispersions is preferably within a range from 1 to 1000 mPas, preferably from 10 to 400 mPas (at a solids content of 40% by weight), as measured with a rotational viscometer in accordance with DIN 53019 at 23xc2x0 C. and a shear rate of 250 sxe2x88x921.
The redispersible polymer powders can be obtained from aqueous polymer dispersions by drying processes, especially spray drying.
For spray drying it is also possible to add drying assistants to the aqueous polymer dispersion, examples being polyvinyl acetate hydrolysates or formaldehyde-naphthalenesulfonic acid condensates.
The spray drying usually takes place in a drying tower.
In general, the spray drying of the aqueous polymer dispersion is conducted at an air stream inlet temperature TI, of from 100 to 200xc2x0 C., preferably 120 to 160xc2x0 C., and an air stream outlet temperature TO of from 30 to 90xc2x0 C., preferably from 50 to 90xc2x0 C. The spraying of the aqueous polymer dispersion in the hot air stream can be carried out, for example, by means of single-fluid or multi-fluid nozzles or via a rotating disk. The polymer powders are normally collected using cyclones or filter separators. The spray-dispensed aqueous polymer dispersion and the hot air stream are preferably guided in parallel. Frequently, a finely divided mineral antiblocking agent (e.g. finely divided silica gel) is metered into the tower during the spray drying operation, especially to suppress any clumping together of the spray-dried secondary polymer particles during prolonged storage of the polymer powder that results in accordance with the invention.
The water-dispersible or water-redispersible polymer can be mixed with cement in the abovementioned amounts at any time, i.e. immediately or not until shortly before use.
The cement involved can be blast furnace cement, oil shale cement, Portland cement, hydrophobicized Portland cement, quicksetting cement, high expansion cement or high alumina cement, although the use of Portland cement has proven particularly advantageous.
Further constituents which may also be present in the compositions of the invention besides cement and polymer dispersion include optional constituents such as, for example, mineral aggregates, such as sand, gravel, silica, microsilica, lime, chalk, gypsum, loam, clay and also defoamers, plasticizers, flow aids and setting retardants or setting accelerators.
Normally, the composition of the invention is mixed with water and then processed.
The compositions are suitable, for example, as repair mortars or reinforcing mortars, and also as tile adhesives, sealants, coating compositions or fillers.
The cement compositions of the invention are notable for the high electrolyte stability of the polymer in the presence of cement. The polymer dispersion as such contains virtually no coagulum and can easily be converted to powder form, e.g., spray-dried.
In aqueous cement compositions, the polymer dispersions exhibit good miscibility and thus result in effective processing. Homogeneous cement slurries are obtained which show no sedimentation (xe2x80x9cbleedingxe2x80x9d) and exhibit little tool tack. The processing period (xe2x80x9copen timexe2x80x9d) of the aqueous cement compositions is sufficient. In the case of customary formulations it is more than 15 minutes, generally more than 30 minutes.
In the hardened cementitious masses, the addition of the polymer results in great flexibilization of the material and increased adhesion to mineral substrates. Polymer-rich compositions containing more than 20% by weight polymer based on the mineral components result in highly flexible, water-resistant films of high cohesion.